Copper alloys have widely been used for materials for a variety of articles such as electric parts because of their excellent properties of electrical conduction and heat conduction. Regarding the copper alloys for casting, various kinds of the copper alloys are standardized in JIS H5120 for a variety of articles such as a valve body, a faucet and a bearing.
The copper alloys for casting are generally used for the faucets of water and sewerage, and for a valve for general plumbing. In particular, in the alloys standardized by JIS H5120, brasses (Cu—Zn system alloy) such as CAC203 of the copper alloy, and bronzes such as CAC403 (Cu—Sn—Zn system alloy) and CAC406 (Cu—Sn—Pb—Zn system alloy) are materials for the articles.
In the case to be used for the faucet and the valve as described above, good properties such as high pressure resistance, wear resistance, castability, mechanical properties (strength and hardness), and machinability are required. Lead (Pb) is commonly contained as the way of improving machinability of the copper alloy, and the machinability of the CAC406 of the above copper alloy for casting is improved as the result of containing lead of about 4-6%, by mass. In addition, it is known that the pressure resistance is also improved by containing lead (ex. NONPATENT LITERATURE 1).
On the other hand, water pollution is caused by dissolving lead into drinking water if a variety of articles such as the faucet and the valve is made by the copper alloy containing lead for casting, and it has been pointed out that the polluted water has harmful effect to a human body. In particular, the regulation of lead in water quality-based limitations was increased by ⅕ of the former value, and the regulation for using lead in the copper alloy for casting used for the articles such as the faucet and the valve has become strict.
Therefore, many kinds of copper alloy for casting improved in machinability have been proposed even though lead is not added into the copper alloys. The copper alloys containing bismuth and/or selenium to improve machinability were developed in western countries, and the alloys have been standardized in CDA (Copper Development Association) (ex. NONPATENT LITERATURE 2). The copper alloy containing Sb with Bi is also known (above NONPATENT LITERATURE 1).
These copper alloys contain Bi, Se and Sb as an element for free cutting instead of lead, and, by the development of the technology, good machinability is provided without the harm of lead.
However, the further improvement of the developed lead free copper alloys is required because the pressure resistance of the alloys can be degraded rather than the conventional standardized copper alloy, due to common occurrence of porosity as casting defect. On the other hand, there are problems in point of views of raw materials and resources because Bi and Se are rare metals (small amount of deposit). The copper alloy having better mechanical properties such as strength and elongation than the conventional leaded copper alloy for casting has never developed.